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300-Million-Year-Old Baby Embolomere Fossils Show No Tadpole Stage but Retained Aquatic Lifestyle
Researchers at the Field Museum examined two 2-centimeter baby embolomere specimens from the Mazon Creek site. The fossils indicate these Carboniferous predators developed directly into adults without metamorphosis.
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Researchers at the Field Museum of Natural History examined two 2-centimeter-long baby embolomere fossils that preserve soft tissues and external egg yolk. The specimens, collected decades earlier at the Mazon Creek site southwest of Chicago, date to 307 million to 309 million years ago. Adult embolomeres reached about 2 meters and ranked among the largest tetrapods of the Carboniferous Period.
The babies already possessed the full suite of skull and skeletal elements found in adults, differing only in size and proportions. The young animals carried an external yolk sac and lacked external gills. Jason Pardo of the Field Museum said the absence of gills constitutes “the smoking gun” against a larval aquatic phase.
Pardo and colleague Arjan Mann also examined fossils of two additional early tetrapod species from the same locality and time. None displayed evidence of a tadpole-like stage. The team concluded that early tetrapod-like fishes living about 308 million years ago did not require metamorphosis to move onto land.
John Long of Flinders University stated the findings show such a phase “was previously thought by some scientists” but is unsupported by the data. The study was published in the journal Science.
